Hydrocarbon-decomposing porous catalyst body and process for producing the same, process for producing hydrogen-containing mixed reformed gas from hydrocarbons, and fuel cell system

ABSTRACT

A process for producing the porous catalyst body for decomposing hydrocarbons, the body containing at least magnesium, aluminum and nickel, and has a pore volume of 0.01 to 0.5 cm 3 /g, an average pore diameter of not more than 300 Å and an average crushing strength of not less than 3 kgf. The process includes molding hydrotalcite containing at least magnesium, aluminum and nickel, and calcining the resulting molded product at a temperature of 700 to 1500° C.

This application is a divisional of application Ser. No. 12/874,505filed Sep. 2, 2010, now allowed, which in turn is a Continuation-In-Partof International Application No. PCT/JP2009/001001 filed 5 Mar. 2009,which designated the U.S. and claims priority of Japan Application Nos.2008-057050 filed 6 Mar. 2008, the entire contents of each of which areall hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention aims at providing a catalyst as a porous catalystbody for decomposing hydrocarbons which comprises at least magnesium,aluminum and nickel, wherein the catalyst is less expensive, and has anexcellent catalytic activity for decomposition and removal ofhydrocarbons, an excellent anti-sulfur poisoning property, an excellentanti-coking property even under a low-steam condition, a sufficientstrength capable of withstanding crushing and breakage even when cokingoccurs within the catalyst, and an excellent durability.

Also, the present invention relates to a porous catalyst body fordecomposing hydrocarbons which comprises at least magnesium, aluminumand nickel, and a process for producing the porous catalyst body, aswell as aims at providing a porous catalyst body for decomposinghydrocarbons which has a large number of micropores, a large specificsurface area, a large pore volume and a high strength, and a process forproducing the porous catalyst body.

In addition, the present invention aims at not only efficientlydecomposing and removing hydrocarbons but also producing hydrogen byusing the above catalyst.

BACKGROUND ART

In recent years, in the consideration of global environmental problems,early utilization techniques for new energies have been intensivelystudied, and fuel cells or batteries have been noticed as one of thesetechniques. In the fuel cells, hydrogen and oxygen are electrochemicallyreacted with each other to convert a chemical energy into an electricenergy. Thus, the fuel cells are characterized by a high energyutilization efficiency and, therefore, have been positively studied forpractical applications to civil life, industries or automobiles. Thefuel cells generally known in the art are classified into a phosphoricacid type (PAFC), a molten carbonate type (MCFC), a solid oxide type(SOFC), a solid polymer type (PEFC), etc., according to kinds ofelectrolytes used therein.

As to the fuel sources for generating hydrogen used in the fuel cells,there have been made various studies on extensive hydrocarbon-containingraw materials including petroleum-based fuels such as kerosene,isooctane and gasoline, LPG or city gases.

As the method of obtaining a reformed gas comprising hydrogen as a maincomponent by reforming the hydrocarbon-containing fuels, there are knownvarious reforming techniques such as SR (steam reforming) method, PDX(partial oxidation) method and SR+PDX (autothermal) method. Among thesereforming techniques, application of the steam-reforming (SR) method tocogeneration has been most noticed, since the SR method enablesproduction of a reformed gas having a high hydrogen concentration.

The steam reforming (SR) is conducted according to the followingreaction formula:

C_(n)H_(2n+2) +nH₂O→nCO+(2n+1)H₂

CO+H₂O→CO₂+H₂

In general, the above reaction is conducted at a temperature of 600 to800° C. and a S/C ratio (steam/carbon ratio) of about 2.0 to about 3.5.In addition, the reaction is an endothermic reaction and, therefore, canbe accelerated as the reaction temperature is increased.

In general, in the fuel cell system, there may be used the process inwhich after a substantially whole amount of sulfur components containedin a fuel is removed therefrom using a desulfurizer, the thusdesulfurized hydrocarbon is then decomposed to obtain a reformed gascomprising hydrogen as a main component, and the resulting reformed gasis introduced into a fuel cell stack. In such a conventional process, areforming catalyst is used to reform the hydrocarbons. However, thereforming catalyst tends to undergo deterioration in catalystperformance during the operation for a long period of time. Inparticular, the reforming catalyst tends to be poisoned with a traceamount of sulfur components slipped through the desulfurizer, resultingin problems such as significant deterioration in catalytic activitythereof. In addition, when C₂ or more hydrocarbons are used as a fuel,the hydrocarbons in the fuel tend to suffer from thermal decomposition,resulting in deposition of carbon on the catalyst, production ofpolycondensates and deterioration in performance of the reformingcatalyst. Also, among these fuel cell systems, the reforming catalystsfor PAFC and PEFC are generally used in the form of a molded productsuch as beads. In this case, if the beads-shaped catalysts suffer fromsignificant coking inside thereof, the catalysts tend to be broken andpowdered, resulting in clogging of a reaction tube therewith.

The fuels such as city gases, LPG, kerosene, gasoline and naphthacomprise not only C₁ but also C₂ or more hydrocarbons. For example, thecity gas 13A comprises about 88.5% of methane, about 4.6% of ethane,about 5.4% of propane and about 1.5% of butane, i.e., comprises, inaddition to methane as a main component thereof, hydrocarbons having 2to 4 carbon atoms in an amount as large as 11.5%. Also, LPG comprisesabout 0.7% of ethane, about 97.3% of propane, about 0.2% of propyleneand about 1.8% of butane, i.e., comprises the C₄ hydrocarbon in anamount of 1.8%. These C₂ or more hydrocarbons tend to be readilythermally decomposed to cause deposition of carbon.

At present, as an active metal species of the steam reforming catalysts,there may be used noble metals such as Pt, Rh, Ru, Ir and Pd, and basemetals such as Ni, Co and Fe. Among these metals, in the considerationof high catalytic activity, there have been mainly used catalystssupporting a metal element such as Ni and Ru.

The noble metals such as Ru tend to hardly undergo deposition of carboneven under a low S/C (steam/carbon) ratio condition. However, the noblemetals tend to be readily poisoned with sulfur components contained inthe raw materials, and deteriorated in catalytic activity for a shortperiod of time. Further, deposition of carbon tends to be extremelyreadily caused on the sulfur-poisoned catalysts. Thus, even in the casewhere the noble metals are used, there also tends to arise such aproblem that deposition of carbon is induced by the poisoning withsulfur. In addition, since the noble metals are expensive, the fuel cellsystems using the noble metals tend to become very expensive, therebypreventing further spread of such fuel cell systems.

On the other hand, since Ni as a base metal element tends to relativelyreadily undergo deposition of carbon, it is required that theNi-containing catalyst is used under a high steam/carbon ratio conditionin which steam is added in an excessive amount as compared to atheoretical compositional ratio thereof, so that the operation proceduretends to become complicated, and the unit requirement of steam tends tobe increased, resulting in uneconomical process. Further, since theconditions for continuous operation of the system are narrowed, in orderto complete the continuous operation of the system using theNi-containing catalyst, not only an expensive control system but also avery complicated system as a whole are required. As a result, theproduction costs and maintenance costs tend to be increased, resultingin uneconomical process.

Since the steam reforming reaction is a high-temperature reaction andthe fuel cell system is subjected to DSS (Daily Start-up and Shutdown)operation, the catalyst body filled in a reactor is gradually closelypacked by repeated expansion/contraction and swelling of the reactorowing to external heating, which tends to finally cause breakage of thecatalyst. For this reason, in the fuel cell system, α-alumina having arelatively high crushing strength has been generally used as a carrierfor the catalyst.

However, the α-alumina has been generally produced by baking a rawmaterial at a high temperature to enhance its crushing strength.Therefore, the resulting α-alumina exhibits an extremely small BETspecific surface area and pore volume. As a result, an active metalspecies supported on the α-alumina tends to be readily sintered whenexposed to heat, resulting in deterioration of its catalytic activity.

When using Ni which is relatively susceptible to deposition of carbon asthe active metal species, an alkaline element such as CaO and MgO may beadded to suppress the deposition of carbon on Ni. However, when thecontent of the alkaline element is too large, the resulting catalysttends to be considerably deteriorated in strength.

In addition, in order to suppress the deposition of carbon, if an MgOcarrier only is subjected to tablet molding or press molding to therebyforcibly increase a strength of the catalyst, the resulting catalysttends to be deteriorated in catalytic activity. As a result, it may bevery difficult to impart a high activity to the catalyst.

For the above-mentioned reasons, it has been demanded to provide ahydrocarbon-decomposing catalyst which is less expensive and can exhibitas its functions an excellent catalytic activity capable of decomposingand removing hydrocarbons, a good anti-coking property even under a lowsteam condition, a sufficient strength capable of withstanding crushingand breakage even when coking occurs within the catalyst, and anexcellent durability.

Conventionally, there have been reported hydrocarbon-decomposingcatalysts formed by supporting a catalytically active metal such asplatinum, palladium, ruthenium, cobalt, rhodium, ruthenium and nickel ona carrier comprising α-alumina, magnesium oxide or titanium oxide(Patent Documents 1 to 4, etc.). Also, there are known the methods forproducing a hydrocarbon-decomposing catalyst by using an Ni-containinghydrotalcite compound as a precursor (Patent Documents 5 to 7, etc.)

-   Patent Document 1: Japanese Patent Application Laid-Open (KOKAI) No.    9-173842-   Patent Document 2: Japanese Patent Application Laid-Open (KOKAI) No.    2001-146406-   Patent Document 3: Japanese Patent Application Laid-Open (KOKAI) No.    2004-82034-   Patent Document 4: Japanese Patent Application Laid-Open (KOKAI) No.    2003-284949-   Patent Document 5: Japanese Patent Application Laid-Open (KOKAI) No.    2000-503624-   Patent Document 6: Japanese Patent Application Laid-Open (KOKAI) No.    2003-135967-   Patent Document 7: Japanese Patent Application Laid-Open (KOKAI) No.    2004-255245

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In the technique of the Patent Document 1, there is described theprocess for producing hydrogen by subjecting fuels comprisinghydrocarbons such as kerosene to steam reforming using a catalystcomprising Ru as an active metal species which is supported on α-aluminaas a carrier. However, it is considered that the Ru-based catalyst tendsto suffer from sulfidization with sulfur components contained in the rawmaterials which results in promoted coking and deactivation of thecatalyst.

In the techniques of the Patent Documents 2 and 3, the obtainedcatalysts are improved in anti-sulfur poisoning property, but stillinsufficient in their catalyst performance.

In the Patent Document 4, there is described the method of producing ahigh strength molded product from MgO solely. However, the resultingmolded product has a very low breaking strength ranging from 0.3 to 1.2kg/mm. Further, it is readily suggested that the BET specific surfacearea and pore volume of the catalyst are small, although notparticularly described therein.

In the techniques of the Patent Documents 5 to 7, there are describedhydrocarbon-decomposing catalysts obtained by using an Ni-containinghydrotalcite compound as a precursor. However, these Patent Documentsfail to take a strength of the catalysts themselves into consideration.

In addition, as the carrier for generally used steam-reformingcatalysts, there have been used γ-alumina, α-alumina, silica, zeolite,etc. However, among these conventional catalysts, there have beenreported no porous catalyst bodies comprising a large amount ofmagnesium and having a large specific surface area and a high crushingstrength.

Further, there has not been reported any method of producing a moldedproduct from hydrotalcite as a precursor.

An object of the present invention is to provide a catalyst as a porouscatalyst body for decomposing hydrocarbons which comprises at leastmagnesium, aluminum and nickel, wherein the catalyst is less expensive,and has an excellent catalytic activity for decomposition and removal ofhydrocarbons, an excellent anti-sulfur poisoning property, an excellentanti-coking property even under a low-steam condition, a sufficientstrength capable of withstanding crushing and breakage even when cokingoccurs within the catalyst, and an excellent durability.

Another object of the present invention is to provide a porous catalystbody for decomposing hydrocarbons which comprises at least magnesium,aluminum and nickel and a process for producing the porous catalystbody, in which the porous catalyst body includes a large number ofmicropores, and has a large specific surface area, a large pore volumeand a high strength, as well as a process for producing the porouscatalyst body.

A further object of the present invention is to provide a process foreffectively decomposing and removing hydrocarbons and producing hydrogenby using the above catalyst.

Means for Solving the Problems

The above-described technical problems can be solved by the followingaspects of the present invention.

That is, according to the present invention, there is provided a porouscatalyst body for decomposing hydrocarbons which comprises at leastmagnesium, aluminum and nickel in such a manner that the magnesium andaluminum are present in the form of a composite oxide of magnesium andaluminum, and the nickel is present in the form of metallic nickel; andwhich porous catalyst body has a magnesium element content of 10 to 50%by weight, an aluminum element content of 5 to 35% by weight and anickel element content of 0.1 to 30% by weight, a pore volume of 0.01 to0.5 cm³/g, an average pore diameter of not more than 300 Å and anaverage crushing strength of not less than 3 kgf. (Invention 1).

Also, according to the present invention, there is provided the porouscatalyst body for decomposing hydrocarbons as described in the aboveInvention 1, wherein the metallic nickel is present in the form of fineparticles having an average particle diameter of 1 to 20 nm (Invention2).

Also, according to the present invention, there is provided the porouscatalyst body for decomposing hydrocarbons as described in the aboveInvention 1 or 2, wherein the porous catalyst body has a BET specificsurface area of 10 to 100 m²/g (Invention 3).

Also, according to the present invention, there is provided a processfor producing the porous catalyst body for decomposing hydrocarbons asdescribed in any one of the above Inventions 1 to 3, which comprises thestep of molding hydrotalcite comprising at least magnesium, aluminum andnickel; and calcining the resulting molded product at a temperature of700 to 1500° C. (Invention 4).

Also, according to the present invention, there is provided the processas described in the above Invention 4, which further comprises the stepof subjecting the calcined hydrotalcite molded product to reductiontreatment at a temperature of 700 to 1000° C. (Invention 5).

Also, according to the present invention, there is provided the porouscatalyst body for decomposing hydrocarbons as described in any one ofthe above Inventions 1 to 3, wherein one or more active metal speciesselected from the group consisting of gold, silver, platinum, palladium,ruthenium, cobalt, rhodium, iridium, rhenium, copper, manganese,chromium, vanadium and titanium which have an average particle diameterof not more than 50 nm, are supported on the porous catalyst body(Invention 6).

Also, according to the present invention, there is provided a processfor producing a mixed reformed gas comprising hydrogen fromhydrocarbons, which comprises the step of reacting the hydrocarbons withsteam at a temperature of 250 to 850° C., at a molar ratio of steam tocarbon (S/C) of 1.0 to 6.0 and at a space velocity (GHSV) of 100 to100000 h⁻¹ by using the porous catalyst body for decomposinghydrocarbons as described in any one of the above Inventions 1, 2, 3 and6 (Invention 7).

In addition, according to the present invention, there is provided afuel cell system using the porous catalyst body for decomposinghydrocarbons as defined in any one of the above Inventions 1, 2, 3 and 6(Invention 8).

EFFECT OF THE INVENTION

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has a large BET specific surface area and a large porevolume and supports metallic nickel in the form of very fine particles.For this reason, the metallic nickel as an active metal species has anincreased contact area with steam, and, therefore, can exhibit anexcellent catalytic activity.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is produced by subjecting the raw materials tohigh-temperature calcination. For this reason, the porous catalyst bodycan maintain a large BET specific surface area and a large pore volumeeven when used under high-temperature condition, and can also maintain ahigh catalytic activity for a long period of time.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has a high crushing strength by formation of a spinelphase comprising magnesium and aluminum, and nickel and aluminum owingto the high-temperature calcination. For this reason, when the porouscatalyst body suffers from coking during the steam reforming reaction,the catalyst molded product can maintain an excellent catalytic activitywithout suffering from breakage and powdering.

As described above, the porous catalyst body for decomposinghydrocarbons according to the present invention has a high catalyticactivity. Therefore, even under a low-steam condition, the porouscatalyst body can exhibit an excellent anti-coking property and a highcatalytic activity.

In addition, the porous catalyst body for decomposing hydrocarbonsaccording to the present invention can be enhanced in catalytic activityand anti-coking property as well as anti-oxidizing property bysupporting an active metal species such as gold, silver, platinum,palladium, ruthenium, cobalt, rhodium, iridium, rhenium, copper,manganese, chromium, vanadium and titanium thereon.

Also, the porous catalyst body for decomposing hydrocarbons according tothe present invention comprises a large amount of magnesium andtherefore exhibits a very excellent anti-sulfur poisoning property aswell as an excellent catalytic activity from the viewpoint of itsdurability.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is described below.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is formed of a compound comprising at least magnesium,aluminum and nickel in which the magnesium and aluminum are present inthe form of a composite oxide of magnesium and aluminum, and the nickelis present in the form of metallic nickel. The porous catalyst body mayalso comprise, in addition to the magnesium, aluminum and nickelelements and oxygen as the composite oxide, other elements such assodium, calcium, silicon, iron and zinc although not particularlylimited thereto.

The content of magnesium in the porous catalyst body for decomposinghydrocarbons according to the present invention is 10 to 50% by weight.When the magnesium content is less than 10% by weight, the resultingporous catalyst body tends to have a small BET specific surface area andfurther tends to be deteriorated in anti-sulfur poisoning property. Onthe other hand, when the magnesium content is more than 50% by weight,the resulting porous catalyst body tends to be deteriorated inmechanical strength. The magnesium content in the porous catalyst bodyis preferably 15 to 45% by weight and more preferably 20 to 40% byweight.

Also, the content of aluminum in the porous catalyst body fordecomposing hydrocarbons according to the present invention is 5 to 35%by weight. When the aluminum content is less than 5% by weight, theresulting porous catalyst body tends to be deteriorated in mechanicalstrength. On the other hand, when the aluminum content is more than 35%by weight, the resulting porous catalyst body tends to have a small BETspecific surface area and, therefore, may fail to form a porousstructure. The aluminum content in the porous catalyst body ispreferably 10 to 30% by weight.

The content of nickel in the porous catalyst body for decomposinghydrocarbons according to the present invention is 0.1 to 30% by weight.When the nickel content is less than 0.1% by weight, the resultingporous catalyst body tends to be deteriorated in conversion rate ofhydrocarbons. On the other hand, when the nickel content is more than30% by weight, the particle size of the metallic nickel fine particlestends to exceed 20 nm, so that the resulting porous catalyst body tendsto be considerably deteriorated in anti-coking property. The nickelcontent in the porous catalyst body is preferably 0.2 to 25% by weight.

The ratio between magnesium and aluminum in the porous catalyst body fordecomposing hydrocarbons according to the present invention is notparticularly limited, and it is preferred that the magnesium be presentin a larger amount than that of the aluminum. The molar ratio of themagnesium to the aluminum (Mg:Al) is preferably 5:1 to 1:1. When theproportion of the magnesium is more than the above-specified range, itmay be difficult to readily obtain a catalyst body having a sufficientstrength. On the other hand, when the proportion of the magnesium isless than the above-specified range, the resulting catalyst body mayfail to exhibit properties as a porous substance.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has a pore volume of 0.01 to 0.5 cm³/g. When the porevolume is less than 0.01 cm³/g, the resulting porous catalyst body mayfail to support and disperse a sufficient amount of active metal speciesthereon. When the pore volume is more than 0.5 cm³/g, the resultingporous catalyst body tends to be deteriorated in mechanical strength.The pore volume of the porous catalyst body is preferably 0.02 to 0.45cm³/g and more preferably 0.05 to 0.40 cm³/g.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has an average pore diameter of not more than 300 Å.When the average pore diameter is more than 300 Å, the resulting porouscatalyst body may fail to support and disperse a sufficient amount ofactive metal species thereon. The average pore diameter of the porouscatalyst body is preferably not more than 290 Å, and more preferably 50to 280 Å.

In the porous catalyst body for decomposing hydrocarbons according tothe present invention, metallic nickel is present in a composite oxideof magnesium and aluminum.

In the porous catalyst body for decomposing hydrocarbons according tothe present invention, the metallic nickel has an average particlediameter of not more than 20 nm and exhibits an excellent catalyticactivity which is optimum for production of hydrogen. When the averageparticle diameter of the metallic nickel is more than 20 nm, theresulting porous catalyst body tends to be deteriorated in catalyticactivity required for the steam-reforming reaction in which hydrogen isproduced by mixing a hydrocarbon gas with steam. The average particlediameter of the metallic nickel is preferably not more than 15 nm andmore preferably not more than 10 nm. The lower limit of the averageparticle diameter of the metallic nickel is about 0.5 nm.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention preferably has a BET specific surface area of 10 to100 m²/g. When the BET specific surface area is less than 10 m²/g, theaverage pore diameter of the resulting porous catalyst body tends to betoo large, so that the porous catalyst body may fail to support anddisperse a sufficient amount of active metal species thereon. The porouscatalyst body having a BET specific surface area of more than 100 m²/gmay be difficult to industrially produce and, therefore, tends to beunpractical. The BET specific surface area of the porous catalyst bodyis more preferably 15 to 80 m²/g and still more preferably 20 to 60m²/g.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has an average crushing strength of not less than 3kgf (29.4 N). When the average crushing strength is less than 3 kgf(29.4 N), the resulting porous catalyst body tends to be cracked orbroken when used at a high temperature, and further tends to suffer frombreakage or powdering when coking occurs with the catalyst. The averagecrushing strength of the porous catalyst body is preferably 4 to 50 kgf(39.2 to 490 N) and more preferably 5 to 40 kgf (49 to 392 N).Meanwhile, the average crushing strength may be measured by the methodas described in Examples below.

In the porous catalyst body for decomposing hydrocarbons as defined inany one of the above Inventions 1 to 3, one or more active metal speciesselected from the group consisting of gold, silver, platinum, palladium,ruthenium, cobalt, rhodium, iridium, rhenium, copper, manganese,chromium, vanadium and titanium which have an average particle diameterof not more than 50 nm may be supported thereon (Invention 6). Bysupporting the above active metal species on the porous catalyst body,it is possible to further increase the amount of hydrocarbonsdecomposed.

The active metal species may be incorporated into the porous catalystbody for decomposing hydrocarbons according to the present inventionsimultaneously with production of the porous catalyst body or may besupported thereon after the production of the porous catalyst body,although not particularly limited thereto. The method of supporting theactive metal species is also not particularly limited, and may includeordinary methods such as spray drying method and impregnation method.

When the average particle diameter of the active metal species such asgold, silver, platinum, palladium, ruthenium, cobalt, rhodium, iridium,rhenium, copper, manganese, chromium, vanadium and titanium is more than50 nm, the effect of supporting the active metal species on the claymineral tends to be hardly attained. The average particle diameter ofthe active metal species is preferably not more than 35 nm and morepreferably not more than 20 nm.

The amount of the active metal species supported on the porous catalystbody for decomposing hydrocarbons is not particularly limited. Forexample, the amount of the active metal species supported on the porouscatalyst body for decomposing hydrocarbons may be in the range of 0.01to 30% by weight based on the weight of the porous catalyst body.

As the method of supporting nickel on the porous catalyst body fordecomposing hydrocarbons according to the present invention, there maybe used various methods. For example, there may be used the method ofsupporting nickel on a porous catalyst body for decomposing hydrocarbonswhich comprises magnesium and aluminum by an ordinary method such as aprecipitation method, a heat impregnation method, a cold impregnationmethod, a vacuum impregnation method, an equilibrium adsorption method,an evaporation-to-dryness method, a competitive adsorption method, anion exchange method, a spray method and a coating method; or the methodin which nickel is incorporated into a spinel crystal structure compoundcomprising magnesium and aluminum to form a solid solution therewith,and then the solid solution is heat-treated to allow metallic nickel todeposit on the spinel carrier comprising magnesium and aluminum.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is preferably produced by the method in which therespective constitutional elements are subjected to co-precipitationreaction to form hydrotalcite particles as a precursor, and then theresulting hydrotalcite particles are baked with heating to form a porouscatalyst body, followed by subjecting the obtained porous catalyst bodyto heat reduction.

There is also known the method in which the hydrotalcite particles arebaked to obtain composite oxide particles, and then the composite oxideparticles are hydrated with an aqueous solution comprising an anion toobtain layered composite hydroxide particles. In the present invention,nickel may also be supported by the following production method. Thehydrotalcite particles on which nickel is supported may be subjected toheat reduction, if required after being baked with heating.

More specifically, the nickel may be supported by the method in whichthe porous catalyst body for decomposing hydrocarbons is impregnatedwith a solution comprising nickel to thereby regenerate a hydrotalcitephase comprising nickel in the vicinity of the surface of the porousoxide particles or a molded product thereof.

In addition, the nickel may also be supported by the method in which theporous catalyst body for decomposing hydrocarbons in which nickel hasbeen allowed to be present on the surface of the respective particlesaccording to the above production method, is further impregnated with asolution comprising nickel to thereby regenerate a hydrotalcite phasecomprising nickel in the vicinity of the surface of the molded product.

Next, the process for producing the porous catalyst body for decomposinghydrocarbons according to the present invention is described.

In the process for producing the porous catalyst body for decomposinghydrocarbons according to the present invention, hydrotalcite compoundparticles comprising magnesium, aluminum and nickel as a precursor aremolded to produce a molded product, and then the resulting moldedproduct is heat-treated in a temperature range of 700 to 1500° C. toobtain the porous catalyst body.

The hydrotalcite compound particles comprising magnesium, aluminum andnickel as used in the present invention are obtained by mixing ananion-containing alkaline aqueous solution with an aqueous solutioncomprising a magnesium raw material, an aluminum raw material and anickel raw material to prepare a mixed solution having a pH value of 7.0to 13.0, aging the resulting mixed solution in a temperature range of 50to 300° C., and then subjecting the resulting mixture to separation byfiltration and drying.

The aging time is not particularly limited, and is 1 to 80 hr,preferably 3 to 24 hr and more preferably 5 to 18 hr. When the agingtime is more than 80 hr, such a growth reaction tends to be industriallydisadvantageous.

The magnesium raw material, the aluminum raw material and the nickel rawmaterial are not particularly limited as long as they are in the form ofa water-soluble material such as a nitric acid salt.

Examples of the magnesium raw material used in the above method includemagnesium oxide, magnesium hydroxide, magnesium oxalate, magnesiumsulfate, magnesium sulfite, magnesium nitrate, magnesium chloride,magnesium citrate, basic magnesium carbonate and magnesium benzoate.

Examples of the aluminum raw material used in the above method includealuminum oxide, aluminum hydroxide, aluminum acetate, aluminum chloride,aluminum nitrate, aluminum oxalate and basic aluminum ammonium sulfate.

Examples of the nickel raw material used in the above method includenickel oxide, nickel hydroxide, nickel sulfate, nickel carbonate, nickelnitrate, nickel chloride, nickel benzoate, basic nickel carbonate,nickel formate, nickel citrate and nickel diammonium sulfate.

The hydrotalcite compound particles comprising magnesium, aluminum andnickel as a precursor of the porous catalyst body for decomposinghydrocarbons according to the present invention preferably have anaverage plate surface diameter of 0.05 to 0.4 μm. When the average platesurface diameter of the hydrotalcite compound particles is less than0.05 μm, it may be difficult to subject the resulting particles toseparation by filtration and washing with water, so that it may bedifficult to industrially produce the hydrotalcite compound particles.On the other hand, when the average plate surface diameter of thehydrotalcite compound particles is more than 0.4 μm, it may be difficultto produce the aimed porous catalyst body for decomposing hydrocarbonstherefrom.

The hydrotalcite compound particles used in the present inventionpreferably have a crystallite size D006 of 0.001 to 0.08 μm. When thecrystallite size D006 of the hydrotalcite compound particles is lessthan 0.001 μm, the viscosity of the resulting water suspension tends tobe too high, so that it may be difficult to industrially produce thehydrotalcite compound particles. When the crystallite size D006 of thehydrotalcite compound particles is more than 0.08 μm, it may bedifficult to produce the aimed porous catalyst body for decomposinghydrocarbons therefrom. The crystallite size D006 of the hydrotalcitecompound particles is more preferably 0.002 to 0.07 μm.

The hydrotalcite compound particles comprising magnesium, aluminum andnickel as used in the present invention preferably have a BET specificsurface area of 3.0 to 300 m²/g. When the BET specific surface area ofthe hydrotalcite compound particles is less than 3.0 m²/g, it may bedifficult to produce the aimed porous catalyst body for decomposinghydrocarbons therefrom. When the BET specific surface area of thehydrotalcite compound particles is more than 300 m²/g, the viscosity ofthe resulting water suspension tends to be too high, and it may also bedifficult to subject the suspension to separation by filtration andwashing with water. As a result, it may be difficult to industriallyproduce the hydrotalcite compound particles. The BET specific surfacearea of the hydrotalcite compound particles is more preferably 5.0 to250 m²/g.

The ratio between magnesium and aluminum in the hydrotalcite comprisingmagnesium, aluminum and nickel as used in the present invention is notparticularly limited. The molar ratio of magnesium to aluminum (Mg:Al)in the hydrotalcite is preferably 4:1 to 1:1.

The particle diameter of secondary agglomerated particles of thehydrotalcite compound particles is 0.1 to 200 μm. When the particlediameter of the secondary agglomerated particles of the hydrotalcitecompound particles is less than 0.1 μm, the resulting particles tend tobe hardly subjected to pulverization treatment. As a result, it may bedifficult to industrially produce the aimed particles. When the particlediameter of the secondary agglomerated particles of the hydrotalcitecompound particles is more than 200 μm, it may be difficult to producethe aimed molded product therefrom. The particle diameter of secondaryagglomerated particles of the hydrotalcite compound particles ispreferably 0.2 to 100 μm.

The pulverization treatment may be carried out using a generalpulverizing device (such as an atomizer, YARIYA and a Henschel mixer).

In the molding step for producing the porous catalyst body fordecomposing hydrocarbons according to the present invention, thehydrotalcite compound particles comprising at least magnesium, aluminumand nickel as a precursor of the porous catalyst body for decomposinghydrocarbons are mixed with a molding assistant and a binder and furtherwith water and an alcohol as a dispersing medium, and the resultingmixture is kneaded using a kneader (such as a screw kneader) to form aclayey mass, followed by molding the resulting clayey mass. As themolding method, there may be used a compression molding method, a pressmolding method, a tablet molding method, etc.

The shape of the molded product of the porous catalyst body fordecomposing hydrocarbons according to the present invention is notparticularly limited and may be any shape suitably used for ordinarycatalysts. Examples of the shape of the molded product include aspherical shape, a cylindrical shape, a hollow cylindrical shape and apellet shape.

The porous catalyst body for decomposing hydrocarbons which has aspherical shape usually has a size of 1 to 10 mmφ and preferably 2 to 8mmφ.

Examples of the molding assistant usable in the above method includecelluloses, polyvinyl alcohol, starches, methyl cellulose, maltose andcarboxymethyl cellulose. These molding assistants may be be used incombination of any two or more thereof. The molding assistant iscompletely burned out by the calcination treatment and thereforedissipated from the porous catalyst body for decomposing hydrocarbonswithout any residues therein. The amount of the molding assistant addedmay be, for example, 1 to 50 parts by weight based on 100 parts byweight of the hydrotalcite compound particles comprising magnesium,aluminum and nickel.

Examples of the binder include those binders having no re-miscibilitywith water such as α-alumina, an aluminum salt, silica, clay, talc,bentonite, zeolite, cordierite, a titania alkali metal salt, an alkaliearth metal salt, a rare earth metal salt, zirconia, mullite, sepiolite,montmorillonite, halloysite, saponite, stevensite, hectorite, and silicaalumina. These binders may be used in combination of any two or morethereof. In the case where a salt other than an oxide is added as thebinder, it is important that the salt is decomposed into an oxide by thecalcination treatment. The amount of the binder added may be, forexample, 1 to 50 parts by weight based on 100 parts by weight of thehydrotalcite compound particles comprising magnesium, aluminum andnickel.

Examples of the alcohols include monohydric alcohols such as ethanol andpropanol; glycols such as ethylene glycol, propylene glycol, butanedioland polyethylene glycol; and polyhydric alcohols such as glycerol. Thesealcohols may be used in combination of any two or more thereof. Theamount of the alcohols added may be, for example, 50 to 150 parts byweight based on 100 parts by weight of the hydrotalcite compoundparticles comprising magnesium, aluminum and nickel.

In addition, a combustible substance may be added to the hydrotalcitecompound particles. Examples of the combustible substance include woodchips, cork particles, coal powder, activated carbon, crystallinecellulose powder, starches, sucrose, gluconic acid, polyethylene glycol,polyvinyl alcohol, polyacrylamide, polyethylene, polystyrene and amixture thereof. As the amount of the above combustible substance addedis increased, the pore volume of the resulting molded product becomeslarger. However, the addition of an excessive amount of the combustiblesubstance tends to result in deteriorated strength of the resultingmolded product. Therefore, the amount of the combustible substance addedmay be suitably controlled in view of a good strength of the resultingmolded product.

Alternatively, the porous catalyst body for decomposing hydrocarbons maybe formed into a honeycomb structure. In such a case, thehoneycomb-shaped molded product may be obtained by an optional methodselected according to the requirements.

The clayey kneaded material molded by the above method may be dried byvarious methods such as air drying, hot air drying and vacuum drying.

The thus dried clayey kneaded material may be further heat-treated toobtain the porous catalyst body for decomposing hydrocarbons accordingto the present invention. The heat treatment may be carried out at atemperature of 700 to 1500° C. When the heat-treating temperature islower than 700° C., the heat treatment tends to require a prolonged timeto ensure a good crushing strength of the resulting porous catalystbody, resulting in industrial disadvantageous process. On the otherhand, when the heat-treating temperature is higher than 1500° C., theresulting porous catalyst body for decomposing hydrocarbons tends tosuffer from collapse of pores therein. The heat-treating temperature ispreferably 800 to 1400° C. and more preferably 900 to 1300° C.

The heat-treating time is 1 to 72 hr. When the heat-treating time isshorter than 1 hr, the resulting porous catalyst body tends to bedeteriorated in crushing strength. When the heat-treating time is longerthan 72 hr, the resulting porous catalyst body for decomposinghydrocarbons tends to suffer from collapse of pores therein, and such aprolonged heat treatment tends to be disadvantageous from industrialviewpoints. The heat-treating time is preferably 2 to 60 hr and morepreferably 3 to 50 hr.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is obtained by subjecting the calcined product of theporous catalyst body for decomposing hydrocarbons to reduction treatmentat a temperature of 700 to 1000° C. When the temperature used in thereduction treatment is lower than 700° C., the nickel tends to be hardlymetalized, so that the resulting porous catalyst body may fail toexhibit a high catalytic activity as aimed by the present invention.When the temperature used in the reduction treatment is higher than1000° C., sintering of the nickel tends to excessively proceed so thatthe particle size of the metallic nickel fine particles tends to be toolarge. As a result, the resulting porous catalyst body tends to bedeteriorated in conversion rate of lower hydrocarbons under alow-temperature condition, and further in anti-coking property. Thetemperature used in the reduction treatment is preferably 700 to 950° C.

The atmosphere used in the reduction treatment is not particularlylimited as long as it is a reducing atmosphere such as ahydrogen-containing gas.

The time of the reduction treatment is not particularly limited and isdesirably 0.5 to 24 hr. When the time of the reduction treatment islonger than 24 hr, the process tends to have no merit from industrialviewpoints. The time of the reduction treatment is preferably 1 to 10hr.

Next, the process for producing a mixed reformed gas comprising hydrogenfrom hydrocarbons according to the present invention is described.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is contacted with hydrocarbons to obtain a mixedreformed gas comprising hydrogen.

In the process for producing a mixed reformed gas comprising hydrogenfrom hydrocarbons according to the present invention, a raw material gascomprising hydrocarbons and steam are contacted with the porous catalystbody for decomposing hydrocarbons according to the present inventionunder the conditions including a temperature of 250 to 850° C., a molarratio of steam to carbons (S/C ratio) of 1.0 to 6.0 and a space velocity(GHSV) of 100 to 100000 h⁻¹.

When the reaction temperature is lower than 250° C., the conversion rateof lower hydrocarbons tends to be reduced, so that when the reaction isconducted for a long period of time, coking tends to be caused, finallyresulting in deactivation of the catalyst. When the reaction temperatureis higher than 850° C., the active metal species tends to suffer fromsintering, so that the catalyst tends to be deactivated. The reactiontemperature is preferably 300 to 700° C. and more preferably 400 to 700°C.

When the molar ratio S/C of steam (S) to carbons (C) is less than 1.0,the anti-coking property tends to be deteriorated. When the molar ratioS/C of steam (S) to carbons (C) is more than 6.0, a large amount ofsteam tends to be required for the production of hydrogen, resulting inhigh production costs and unpractical process. The molar ratio S/C ispreferably 1.5 to 6.0 and more preferably 1.8 to 5.0.

Meanwhile, the space velocity (GHSV) is preferably 100 to 100000 h⁻¹ andmore preferably 1000 to 10000 h⁻¹.

The hydrocarbons used in the present invention are not particularlylimited, and various hydrocarbons may be used therein. Examples of thehydrocarbons may include saturated aliphatic hydrocarbons such asmethane, ethane, propane, butane, pentane, hexane and cyclohexane;unsaturated hydrocarbons such as ethylene, propylene and butene;aromatic hydrocarbons such as benzene, toluene and xylene; and mixturesof these compounds. Also, suitable examples of the industrially usableraw materials may include city gas 13A, natural gases, LPG, kerosene,gasoline, light oils and naphtha.

When the hydrocarbons used in the present invention are those kept in aliquid state at room temperature such as kerosene, gasoline and lightoils, such hydrocarbons may be vaporized by an evaporator upon use.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention can exhibit sufficient catalytic activity, durability,anti-coking property and anti-sulfur poisoning property even in the casewhere the decomposition process is started by an autothermal reformingreaction and then changed to steam reforming reaction which is furthercontinued for a long period of time. Therefore, the porous catalyst bodyof the present invention can provide an optimum catalyst for fuel cellsystems into which DSS (Daily Start-up and Shutdown) is introduced.

<Function>

The reason why the porous catalyst body for decomposing hydrocarbonsaccording to the present invention can exhibit a large specific surfacearea, a large pore volume and a high crushing strength and is excellentin catalytic activity, anti-sulfur poisoning property and anti-cokingproperty, is considered by the present inventor as follows.

That is, the porous catalyst body for decomposing hydrocarbons accordingto the present invention is produced by subjecting a precursor obtainedby molding hydrotalcite in the form of a laminar composite hydroxide tocalcination treatment. Therefore, even when being subjected to thehigh-temperature calcination treatment, water included in thehydrotalcite is removed therefrom to produce an oxide of magnesium,aluminum and nickel which includes a large number of micropores. Forthis reason, the resulting porous catalyst body has very large specificsurface area and pore volume. In addition, since water or carbonic ionsbeing present between layers of the hydrotalcite are eliminated by thecalcination treatment to form pores, the pore size of pores formed inthe porous catalyst body can be reduced.

For the above reason, the porous catalyst body for decomposinghydrocarbons according to the present invention can maintain a largespecific surface area even when calcined at a high temperature and,therefore, can exhibit a high crushing strength by the calcination.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention can exhibit a higher crushing strength owing toformation of a spinel phase comprising magnesium and aluminum, andnickel and aluminum upon being subjected to the high-temperaturecalcination.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has an excellent catalytic activity because metallicnickel in the form of very fine particles is supported thereon so thatthe contact area of the metallic nickel as an active metal species withsteam is enhanced.

In addition, as described above, the porous catalyst body fordecomposing hydrocarbons according to the present invention has a highcatalytic activity and, therefore, can exhibit an excellent anti-cokingproperty and a high catalytic activity even under a low-steam condition.

Further, the porous catalyst body for decomposing hydrocarbons accordingto the present invention can be enhanced in catalytic activity andanti-coking property and further in anti-oxidizing property bysupporting an active metal species such as gold, silver, platinum,palladium, ruthenium, cobalt, rhodium, iridium, rhenium, copper,manganese, chromium, vanadium and titanium thereon.

Furthermore, the porous catalyst body for decomposing hydrocarbonsaccording to the present invention comprises a large amount of magnesiumand, therefore, is extremely excellent in anti-sulfur poisoning propertyand also excellent in catalytic activity from the viewpoint of itsdurability.

EXAMPLES

Typical embodiments and examples of the present invention are asfollows.

The BET specific surface area was measured by nitrogen BET method.

The average pore diameter and the pore volume were determined by BJHmethod using “TriStar 3000” manufactured by Shimadzu Seisakusho Corp.

The crushing strength of the catalyst molded product was determined froman average value of strengths of the 100 catalyst molded products whichwere measured using a digital force gauge manufactured by IMADA K.K.according to JIS Z 8841 (Granules and Agglomerates-Test Methods forStrength).

The particle size of each of metallic nickel, gold, silver, platinum,palladium, ruthenium, cobalt, rhodium, iridium, rhenium, copper,manganese, chromium, vanadium and titanium was expressed by an averagevalue of the particle sizes measured by an electron microscope. Theparticle size of the metal fine particles which was more than 10 nm wascalculated according to the Scherrer's formula from particle sizesthereof measured using an X-ray diffractometer “RINT 2500” manufacturedby Rigaku Denki Co., Ltd., (tube: Cu; tube voltage: 40 kV; tube current:300 mA; goniometer: wide-angle goniometer; sampling width: 0.020°;scanning speed: 2°/min; light-emitting slit: 1°; scattering slit: 1°;light-receiving slit: 0.50 mm). The particle size of each of metallicnickel, gold, silver, platinum, palladium, ruthenium, cobalt, rhodium,iridium, rhenium, copper, manganese, chromium, vanadium and titaniumwhich was determined using the X-ray diffractometer was the same as thatmeasured using the electron microscope.

The content of each of magnesium, aluminum, nickel, gold, silver,platinum, palladium, ruthenium, cobalt, rhodium, iridium, rhenium,copper, manganese, chromium, vanadium and titanium was determined asfollows. That is, a sample was dissolved in an acid, and the resultingsolution was analyzed by a plasma emission spectroscopic device(“SPS-4000” manufactured by Seiko Denshi Kogyo Co., Ltd.).

Typical examples of the present invention are described below.

Example 1 Production of Hydrotalcite Compound Particles

MgSO₄.7H₂O, Al₂(SO₄)₃.8H₂O and NiSO₄.6H₂O were weighed in amounts of1927.7 g, 1001.2 g and 541.2 g, respectively, and dissolved in purewater to prepare 12000 ml of a mixed solution thereof. Separately, 8044mL of an NaOH solution (concentration: 14 mol/L) were mixed with asolution in which 305.5 g of Na₂CO₃ were dissolved, to prepare 23000 mLof an alkali mixed solution. Then, the thus prepared alkali mixedsolution was mixed with the mixed solution comprising the abovemagnesium salt, aluminum salt and nickel salt, and the resultingsolution was aged at 95° C. for 8 hr to obtain a hydrotalcite compound.The resulting hydrotalcite compound was separated by filtration, dried,and then pulverized to obtain hydrotalcite compound particles. As aresult, it was confirmed that the thus obtained hydrotalcite compoundparticles had a BET specific surface area of 43.2 m²/g, and thesecondary agglomerated particles thereof obtained after being subjectingto the pulverization treatment had an average particle diameter of 13.7μm.

<Production of Porous Catalyst Body for Decomposing Hydrocarbons>

Next, 1058.7 g of the thus obtained hydrotalcite compound particles weremixed with 127.1 g of boehmite, 121.2 g of PVA, 105.8 g of water and741.1 g of propylene glycol, and the resulting mixture was kneaded usinga screw kneader for 5 hr. The thus obtained clayey kneaded material wasformed into a 5.1 mmφ spherical shape by a compression molding method,and the resulting spherical molded product was dried at 105° C. and thenheat-treated at 1100° C. for 3 hr. Thereafter, the resulting moldedproduct was subjected to reduction treatment at 780° C. in a gas flowcomprising hydrogen and argon at a volume ratio of 10/90 for 3 hr,thereby obtaining a porous catalyst body for decomposing hydrocarbons.

As a result, it was confirmed that the resulting spherical (diameter:4.5 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 58.5 m²/g, an average pore diameter of 166 Åand a pore volume of 0.185 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 25.07% by weight, the Al content therein was 22.48%by weight, the Ni content therein was 15.93% by weight, the size ofmetallic nickel fine particles therein was 7.8 nm, and the averagecrushing strength thereof was 32.6 kgf.

<Reaction Using the Porous Catalyst Body for Decomposing Hydrocarbons>

The performance of the obtained porous catalyst body for decomposinghydrocarbons was evaluated as follows. That is, 10 to 50 g of the porouscatalyst body was filled in a stainless steel reaction tube having adiameter of 20 mm to prepare a catalyst-filled tube.

A raw material gas and steam were flowed through the catalyst-filledtube (reactor) under the conditions including a reaction pressure of 0.1MPa, a reaction temperature of 300 to 800° C. and a space velocity of10000 h⁻¹. At this time, the ratio of steam to carbon was 1.0, and theratio of steam to carbon was 3.0. Meanwhile, the reaction was conductedusing a city gas (13A) as the raw material gas comprising hydrocarbons.

Since C₂ or more hydrocarbons were decomposed into methane, CO, CO₂ andH₂, the catalyst performance was evaluated using a C_(n) conversion rate(conversion rate of whole hydrocarbons). Also, when using the city gas(13A) as the raw material gas, a conversion rate of the C₂ or morehydrocarbons (such as ethane, propane, butane and pentane) in the rawmaterial gas was calculated and regarded as a conversion rate of thecity gas (13A).

Example

In the case where propane was used as the raw material gas:

Conversion Rate of Propane=100×(CO+CO₂+CH₄+C₂H₆)/(CO+CO₂+CH₄+C₂H₆+C₃H₈)

C_(n) Conversion Rate(Conversion Rate of WholeHydrocarbons)=(CO+CO₂)/(CO+CO₂+CH₄+C₂H₆+C₃H₈)

The catalyst performances of the porous catalyst bodies for decomposinghydrocarbons including hydrocarbons are shown in Tables 1 and 2.

In Table 1, there is shown the relationship between the reactiontemperature (300 to 700° C.) and the conversion rate when the reactionwas conducted using a city gas (13A) as the raw material gas under theconditions including a space velocity (GHSV) of 3000 h⁻¹ and 50000 h⁻¹,a ratio of steam to carbon (S/C) of 3.0 and a reaction time of 24 hr.

In Table 2, there is shown the relationship between the reaction time,the conversion rate of propane and the amounts of carbon depositedbefore and after measurement of the catalytic activity, when thereaction was conducted using a city gas (13A) as the raw material gasunder the conditions including a space velocity (GHSV) of 3000 h⁻¹, areaction temperature of 700° C. and a ratio of steam to carbon (S/C) of1.5, as well as the relationship between the reaction time, crushingstrength, BET specific surface area and pore volume when the ratio ofsteam to carbon (S/C) was 1.5.

Example 2

MgCl₂.6H₂O, AlCl₃.9H₂O and NiCl₂.6H₂O were weighed in amounts of 5619.8g, 741.5 g and 142.9 g, respectively, and dissolved in pure water toprepare 12000 ml of a mixed solution thereof. Separately, 9924 mL of anNaOH solution (concentration: 14 mol/L) were mixed with a solution inwhich 455.8 g of Na₂CO₃ were dissolved, to prepare 28000 mL of an alkalimixed solution. Then, the thus prepared alkali mixed solution was mixedwith the mixed solution comprising the above magnesium salt, aluminumsalt and nickel salt, and the resulting solution was aged at 180° C. for8 hr to obtain a hydrotalcite compound. The resulting hydrotalcitecompound was separated by filtration, dried, and then pulverized toobtain hydrotalcite compound particles. As a result, it was confirmedthat the thus obtained hydrotalcite compound particles had a BETspecific surface area of 12.2 m²/g, and the secondary agglomeratedparticles thereof obtained after being subjected to the pulverizationtreatment had an average particle diameter of 32.2 μm.

Next, 2601 g of the thus obtained hydrotalcite compound particles weremixed with 78.05 g of talc, 546.3 g of starch, 1170.6 g of water and780.5 g of ethylene glycol, and the resulting mixture was kneaded usinga screw kneader for 1.5 hr. The thus obtained clayey kneaded materialwas formed into a 5.2 mmφ spherical shape by a press molding method, andthe resulting spherical molded product was dried at 120° C. and thenheat-treated at 1250° C. for 10 hr. Thereafter, the resulting moldedproduct was subjected to reduction treatment at 850° C. in a gas flowcomprising hydrogen and argon at a volume ratio of 90/10 for 1.5 hr,thereby obtaining a porous catalyst body for decomposing hydrocarbons.

As a result, it was confirmed that the resulting spherical (diameter:2.6 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 11.9 m²/g, an average pore diameter of 208 Åand a pore volume of 0.112 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 44.65% by weight, the Al content therein was 10.78%by weight, the Ni content therein was 2.344% by weight, the size ofmetallic nickel fine particles therein was 2.2 nm, and the averagecrushing strength thereof was 48.2 kgf.

Example 3

Mg(NO₃)₂.6H₂O, Al(NO₃)₃.9H₂O and Ni(NO₃)₂.6H₂O were weighed in amountsof 864.3 g, 549.8 g and 639.2 g, respectively, and dissolved in purewater to prepare 10000 ml of a mixed solution thereof. Separately, 2638mL of an NaOH solution (concentration: 14 mol/L) were mixed with asolution in which 217.5 g of Na₂CO₃ were dissolved, to prepare 24000 mLof an alkali mixed solution. Then, the thus prepared alkali mixedsolution was mixed with the mixed solution comprising the abovemagnesium salt, aluminum salt and nickel salt, and the resultingsolution was aged at 70° C. for 6 hr to obtain a hydrous compositehydroxide. The resulting hydrous composite hydroxide was separated byfiltration, dried, and then pulverized to obtain hydrotalcite compoundparticles. As a result, it was confirmed that the thus obtainedhydrotalcite compound particles had a BET specific surface area of 119.2m²/g, and the secondary agglomerated particles thereof obtained afterbeing subjected to the pulverization treatment had an average particlediameter of 52.1 μm.

Next, 642.8 g of the thus obtained hydrotalcite compound particles weremixed with 35.35 g of γ-alumina, 60.75 g of methyl cellulose, 128.6 g ofwater and 385.7 g of ethylene glycol, and the resulting mixture waskneaded using a screw kneader for 2 hr. The thus obtained clayey kneadedmaterial was formed into a 2.1 mmφ cylindrical shape by an extrusionmolding method, and the resulting cylindrical molded product was driedat 120° C. and then heat-treated at 750° C. for 18 hr. Thereafter, theresulting molded product was subjected to reduction treatment at 730° C.in a gas flow comprising hydrogen and argon at a volume ratio of 50/50for 4.5 hr, thereby obtaining a porous catalyst body for decomposinghydrocarbons.

As a result, it was confirmed that the resulting cylindrical (diameter:1.8 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 98.5 m²/g, an average pore diameter of 82.4 Åand a pore volume of 0.462 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 18.21% by weight, the Al content therein was 21.74%by weight, the Ni content therein was 28.69% by weight, the size ofmetallic nickel fine particles therein was 3.5 nm, and the averagecrushing strength thereof was 3.3 kgf.

Example 4

MgSO₄.7H₂O, Al₂(SO₄)₃.8H₂O and NiSO₄.6H₂O were weighed in amounts of3223.3 g, 1272.1 g and 1100.3 g, respectively, and dissolved in purewater to prepare 15000 ml of a mixed solution thereof. Separately, 4552mL of an NaOH solution (concentration: 14 mol/L) were mixed with asolution in which 388.3 g of Na₂CO₃ were dissolved, to prepare 23000 mLof an alkali mixed solution. Then, the thus prepared alkali mixedsolution was mixed with the mixed solution comprising the abovemagnesium salt, aluminum salt and nickel salt, and the resultingsolution was aged at 80° C. for 6 hr to obtain a hydrotalcite compound.The resulting hydrotalcite compound was separated by filtration, dried,and then pulverized to obtain hydrotalcite compound particles. As aresult, it was confirmed that the thus obtained hydrotalcite compoundparticles had a BET specific surface area of 72.4 m²/g, and thesecondary agglomerated particles thereof obtained after being subjectedto the pulverization treatment had an average particle diameter of 2.2μm.

Next, 1701 g of the thus obtained hydrotalcite compound particles weremixed with 144.6 g of kaolinite, 160.8 g of PVA, 85.08 g of water and1395.3 g of propylene glycol, and the resulting mixture was kneadedusing a screw kneader for 8 hr. The thus obtained clayey kneadedmaterial was formed into a 4.9 mmφ spherical shape by a compressionmolding method, and the resulting spherical molded product was dried at105° C. and then heat-treated at 1050° C. for 12 hr. Thereafter, theresulting molded product was subjected to reduction treatment at 880° C.in a gas flow comprising hydrogen and argon at a volume ratio of 95/5for 8 hr, thereby obtaining a porous catalyst body for decomposinghydrocarbons.

As a result, it was confirmed that the resulting spherical (diameter:3.8 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 27.5 m²/g, an average pore diameter of 122 Åand a pore volume of 0.142 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 27.30% by weight, the Al content therein was 14.72%by weight, the Ni content therein was 21.11% by weight, the size ofmetallic nickel fine particles therein was 18.5 nm, and the averagecrushing strength thereof was 17.4 kgf.

Example 5

MgCl₂.6H₂O, AlCl₃.9H₂O, NiCl₂.6H₂O and CoCl₂.6H₂O were weighed inamounts of 1597.3 g, 431.1 g, 664.8 g and 169.9 g, respectively, anddissolved in pure water to prepare 8000 ml of a mixed solution thereof.Separately, 4755 mL of an NaOH solution (concentration: 14 mol/L) weremixed with a solution in which 265.0 g of Na₂CO₃ were dissolved, toprepare 22000 mL of an alkali mixed solution. Then, the thus preparedalkali mixed solution was mixed with the mixed solution comprising theabove magnesium salt, aluminum salt, nickel salt and cobalt salt, andthe resulting solution was aged at 140° C. for 10 hr to obtain ahydrotalcite compound. The resulting hydrotalcite compound was separatedby filtration, dried, and then pulverized to obtain hydrotalcitecompound particles. As a result, it was confirmed that the thus obtainedhydrotalcite compound particles had a BET specific surface area of 13.2m²/g, and the secondary agglomerated particles thereof obtained afterbeing subjected to the pulverization treatment had an average particlediameter of 22.2 μm.

Next, 1134 g of the thus obtained hydrotalcite compound particles weremixed with 34.03 g of talc, 158.8 g of PVA, 260.9 g of water and 680.6 gof ethylene glycol, and the resulting mixture was kneaded using a screwkneader for 3.3 hr. The thus obtained clayey kneaded material was formedinto a 10 mmφ spherical shape by a press molding method, and theresulting spherical molded product was dried at 120° C. and thenheat-treated at 1150° C. for 10 hr. Thereafter, the resulting moldedproduct was subjected to reduction treatment at 810° C. in a gas flowcomprising hydrogen and argon at a volume ratio of 90/10 for 3.5 hr,thereby obtaining a porous catalyst body for decomposing hydrocarbons.

As a result, it was confirmed that the resulting spherical (diameter:6.5 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 17.5 m²/g, an average pore diameter of 251 Åand a pore volume of 0.121 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 26.65% by weight, the Al content therein was 13.01%by weight, the Ni content therein was 22.63% by weight, the Co contenttherein was 5.681% by weight, the size of metallic nickel fine particlestherein was 9.8 nm, the size of metallic cobalt fine particles thereinwas 12.2 nm, and the average crushing strength thereof was 34.2 kgf.

Example 6

The clayey kneaded material was formed into a 5.2 mmφ spherical shape inthe same manner as defined in Example 1. The resulting spherical moldedproduct was dried at 120° C. and then heat-treated at 1000° C. for 8 hr.Thereafter, Ru was sprayed and supported on the resulting molded productsuch that the amount of Ru supported was 2.2% by weight in terms ofmetallic Ru. After being dried, the resulting product was subjected toreduction treatment at 760° C. in a gas flow comprising hydrogen andargon at a volume ratio of 10/90 for 2 hr.

As a result, it was confirmed that the resulting spherical (diameter:4.7 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 41.5 m²/g, an average pore diameter of 138 Åand a pore volume of 0.161 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 24.52% by weight, the Al content therein was 21.98%by weight, the Ni content therein was 15.58% by weight, the Ru contenttherein was 2.182% by weight, the size of metallic nickel fine particlestherein was 5.5 nm, the size of metallic ruthenium fine particlestherein was 6 nm, and the average crushing strength thereof was 15.4kgf.

Example 7

Mg(NO₃)₂.6H₂O and Al(NO₃)₃.9H₂O were weighed in amounts of 1523.1 g and618.9 g, respectively, and dissolved in pure water to prepare 10000 mlof a mixed solution thereof. Separately, 2400 mL of an NaOH solution(concentration: 14 mol/L) were mixed with a solution in which 244.9 g ofNa₂CO₃ were dissolved, to prepare 15000 mL of an alkali mixed solution.Then, the thus prepared alkali mixed solution was mixed with the mixedsolution comprising the above magnesium salt and aluminum salt, and theresulting solution was aged at 85° C. for 4 hr to obtain a hydrouscomposite hydroxide. The resulting hydrous composite hydroxide wasseparated by filtration, dried, and then pulverized to obtainhydrotalcite compound particles. As a result, it was confirmed that thethus obtained hydrotalcite compound particles had a BET specific surfacearea of 86.5 m²/g, and the secondary agglomerated particles thereofobtained after being subjected to the pulverization treatment had anaverage particle diameter of 42.1 μm.

Next, 487.6 g of the thus obtained hydrotalcite compound particles weremixed with 41.17 g of γ-alumina, 49.41 g of methyl cellulose, 179.7 g ofwater and 396.8 g of ethylene glycol, and the resulting mixture waskneaded using a screw kneader for 1.5 hr. The thus obtained clayeykneaded material was formed into a 2.5 mmφ cylindrical shape by anextrusion molding method, and the resulting cylindrical molded productwas dried at 95° C. and then heat-treated at 950° C. for 20 hr.

Thereafter, a nickel salt was sprayed and supported on the resultingmolded product such that the amount of Ni supported was 8.0% by weightin terms of metallic Ni. After being dried, the resulting product wassubjected to reduction treatment at 760° C. in a gas flow comprisinghydrogen and argon at a volume ratio of 50/50 for 5 hr, therebyobtaining a porous catalyst body for decomposing hydrocarbons.

As a result, it was confirmed that the resulting cylindrical (diameter:2.1 mmφ) porous catalyst body for decomposing hydrocarbons had a BETspecific surface area of 78.5 m²/g, an average pore diameter of 102.4 Åand a pore volume of 0.371 cm³/g. In addition, as a result of analysisof the resulting porous catalyst body, it was confirmed that the Mgcontent therein was 29.61% by weight, the Al content therein was 22.73%by weight, the Ni content therein was 7.944% by weight, the size ofmetallic nickel fine particles therein was 4.2 nm, and the averagecrushing strength thereof was 8.2 kgf.

Comparative Example 1

A mixture obtained by mixing 895.6 g of MgO, 9.652 g of γ-alumina, 71.52g of PVA and 521.3 g of water with each other was kneaded together usinga screw kneader for 1 hr. The thus obtained clayey kneaded material wasformed into a 5.1 mmφ spherical shape by a compression molding method,and the resulting spherical molded product was dried at 120° C. and thenheat-treated at 1250° C. for 8 hr. Thereafter, Ni was sprayed andsupported on the resulting molded product such that the amount of Nisupported was 34% by weight in terms of metallic Ni. After being dried,the resulting product was subjected to reduction treatment at 800° C. ina gas flow comprising hydrogen and argon at a volume ratio of 10/90 for3 hr. As a result, it was confirmed that the resulting spherical(diameter: 3.2 mmφ) catalyst body had a BET specific surface area of 2.2m²/g, an average pore diameter of 382 Å and a pore volume of 0.009cm³/g. In addition, as a result of analysis of the resulting catalystbody, it was confirmed that the Mg content therein was 39.77% by weight,the Al content therein was 0.563% by weight, the Ni content therein was33.33% by weight, the size of metallic nickel fine particles therein was35.5 nm, and the average crushing strength thereof was 4.3 kgf.

Comparative Example 2

A mixture obtained by mixing 845.3 g of γ-alumina and 22.54 g of PVA wasgranulated while spraying pure water thereover using a rollinggranulator, thereby obtaining a spherical γ-alumina molded producthaving a diameter of 4.8 mmφ. The thus obtained spherical molded productwas dried at 120° C. and then heat-treated at 850° C. for 10 hr.Thereafter, Ni was sprayed and supported on the resulting molded productsuch that the amount of Ni supported was 20% by weight in terms ofmetallic Ni. After being dried, the resulting product was subjected toreduction treatment at 780° C. in a gas flow comprising hydrogen andargon at a volume ratio of 10/90 for 2 hr. As a result, it was confirmedthat the resulting spherical (diameter: 2.7 mmφ) catalyst body had a BETspecific surface area of 185.5 m²/g, an average pore diameter of 322 Åand a pore volume of 0.532 cm³/g. In addition, it was confirmed that theAl content in the catalyst body was 42.96% by weight, the Ni contenttherein was 18.79% by weight, the size of metallic nickel fine particlestherein was 25.5 nm, and the average crushing strength thereof was 1.2kgf.

Comparative Example 3

A mixture obtained by mixing 847.2 g of the hydrotalcite compoundparticles obtained in Example 1 and 440.4 g of water with each other waskneaded together using a screw kneader for 5 hr. The thus obtainedclayey kneaded material was formed into a 5.3 mmφ spherical shape by acompression molding method, and the resulting spherical molded productwas dried at 105° C. and then heat-treated at 1100° C. for 3 hr.Thereafter, the resulting product was subjected to reduction treatmentat 780° C. in a gas flow comprising hydrogen and argon at a volume ratioof 10/90 for 3 hr, thereby obtaining a porous catalyst body fordecomposing hydrocarbons. As a result, it was confirmed that theresulting spherical (diameter: 4.5 mmφ) porous catalyst body fordecomposing hydrocarbons had a BET specific surface area of 65.2 m²/g,an average pore diameter of 144 Å and a pore volume of 0.198 cm³/g. Inaddition, as a result of analysis of the resulting catalyst body, it wasconfirmed that the Mg content therein was 29.42% by weight, the Alcontent therein was 17.19% by weight, the Ni content therein was 18.71%by weight, the size of metallic nickel fine particles therein was 6.5nm, and the average crushing strength thereof was 1.1 kgf.

TABLE 1 GHSV = 3000 h⁻¹ GHSV = 50000 h⁻¹ Reaction 13A 13A temperatureconversion conversion (° C.) rate (%) rate (%) Examples Example 1 30010.04 9.93 400 22.68 22.6 500 45.98 45.87 600 78.24 78.12 700 97.3 97.22Example 2 300 10.04 9.92 400 22.69 22.54 500 45.97 45.84 600 87.2 78.06700 97.29 97.17 Example 3 300 10.02 9.94 400 22.67 22.57 500 45.94 45.81600 78.21 78.06 700 97.28 97.08 Example 4 300 10.03 9.96 400 22.68 22.61500 45.95 45.85 600 78.21 78.04 700 97.27 97.11 Example 5 300 10.0510.02 400 22.7 22.65 500 45.98 45.93 600 78.24 78.21 700 97.3 97.29Examples and Comparative Examples Example 6 300 10.05 10.04 400 22.722.71 500 45.97 45.94 600 78.21 78.17 700 97.3 97.28 Example 7 300 10.0210.02 400 22.65 22.68 500 45.95 45.92 600 78.19 78.11 700 97.28 97.26Comparative 300 6.23 4.85 Example 1 400 14.19 11.65 500 30.11 24.62 60063.29 55.93 700 82.15 74.26 Comparative 300 6.05 4.12 Example 2 40012.71 9.28 500 28.04 23.16 600 60.74 51.12 700 79.05 70.94 Comparative300 10.01 9.89 Example 3 400 22.65 22.58 500 45.95 45.86 600 78.19 78.08700 97.18 97.21

TABLE 2 S/C = 1.5 Amount of 13A carbon Reaction time conversiondeposited Examples (h) rate (%) (wt %) Example 1 12 86.46 0.03 200 86.640.05 300 86.43 0.11 Example 2 12 86.45 0.07 100 86.44 0.09 200 86.430.13 Example 3 12 86.45 0.05 100 86.44 0.07 200 86.42 0.14 Example 4 1286.43 0.08 100 86.44 0.09 200 86.44 0.13 Example 5 12 86.46 0.02 10086.45 0.03 200 86.46 0.03 BET specific Pore Crushing Reaction surfacearea volume strength Examples time (h) (m²/g) (cm³/g) (kgf) Example 1 1258.5 0.185 32.6 200 58.5 0.186 32.5 300 58.4 0.185 32.7 Example 2 1211.9 0.112 48.2 100 11.8 0.112 48.1 200 11.6 0.111 48.7 Example 3 1298.5 0.462 3.3 100 98.3 0.461 3.3 200 97.9 0.442 3.3 Example 4 12 27.50.142 17.4 100 27.5 0.141 17.6 200 27.5 0.142 17.2 Example 5 12 17.50.121 34.2 100 17.5 0.121 34.4 200 17.5 0.119 34.1 S/C = 1.5 Amount ofExamples and 13A carbon Comparative Reaction time conversion depositedExamples (h) rate (%) (wt %) Example 6 12 86.46 0.01 100 86.46 0.02 20086.46 0.02 Example 7 12 86.43 0.06 100 86.46 0.08 200 86.45 0.16Comparative 12 55.21 2.56 Example 1 100 35.69 4.58 200 14.52 9.85Comparative 12 43.26 5.74 Example 2 100 24.13 8.19 200 10.52 12.25Comparative 12 86.42 0.04 Example 3 100 86.43 0.06 200 86.41 0.12 BETspecific Pore Crushing Reaction surface area volume strength Examplestime (h) (m²/g) (cm³/g) (kgf) Example 6 12 41.5 0.161 15.4 100 41.50.158 15.6 200 41.6 0.159 15.7 Example 7 12 78.5 0.371 8.2 100 78.40.368 8.3 200 78.3 0.364 8.5 Comparative 12 2.2 0.009 4.3 Example 1 1002.1 0.008 3.5 200 1.8 0.008 3.2 Comparative 12 185.5 0.532 1.2 Example 2100 102.3 0.362 0.9 200 65.4 0.214 0.7 Comparative 12 65.2 0.198 1.1Example 3 100 64.3 0.195 0.9 200 63.8 0.193 0.7

INDUSTRIAL APPLICABILITY

The porous catalyst body for decomposing hydrocarbons according to thepresent invention has a large BET specific surface area and a large porevolume, and metallic nickel is supported thereon in the form of veryfine particles. Therefore, in the porous catalyst body of the presentinvention, a contact area of the metallic nickel as an active metalspecies with steam is increased, resulting in excellent catalyticactivity of the resulting catalyst.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is produced by high-temperature calcination.Therefore, the porous catalyst body can maintain a large BET specificsurface area and a large pore volume as well as can exhibit an excellentcatalytic activity for a long period of time even when exposed tohigh-temperature conditions.

The porous catalyst body for decomposing hydrocarbons according to thepresent invention is formed with a spinel phase comprising magnesium andaluminum, and nickel and aluminum owing to the high-temperaturecalcination, and therefore exhibits a high crushing strength. Thus, theporous catalyst body can maintain an excellent catalytic activitywithout breakage and powdering thereof even when coking occurs duringthe steam reforming reaction.

In addition, as described above, the porous catalyst body fordecomposing hydrocarbons according to the present invention has a highcatalytic activity, and therefore can exhibit an excellent anti-cokingproperty and a high catalytic activity even under a low-steam condition.

1.-3. (canceled)
 4. A process for producing the porous catalyst body fordecomposing hydrocarbons which comprises at least magnesium, aluminumand nickel in such a manner that the magnesium and aluminum are presentin the form of a composite oxide of magnesium and aluminum, and thenickel is present in the form of metallic nickel; and which porouscatalyst body has a magnesium element content of 10 to 50% by weight, analuminum element content of 5 to 35% by weight and a nickel elementcontent of 0.1 to 30% by weight, a pore volume of 0.01 to 0.5 cm³/g, anaverage pore diameter of not more than 300 Å and an average crushingstrength of not less than 3 kgf, the process comprising the steps of:molding hydrotalcite comprising at least magnesium, aluminum and nickel;and calcining the resulting molded product at a temperature of 700 to1500° C.
 5. A process according to claim 4, further comprising the stepof subjecting the calcined hydrotalcite molded product to reductiontreatment at a temperature of 700 to 1000° C.
 6. (canceled)
 7. A processfor producing a mixed reformed gas comprising hydrogen fromhydrocarbons, comprising the step of reacting the hydrocarbons withsteam at a temperature of 250 to 850° C., at a molar ratio of steam tocarbon (S/C) of 1.0 to 6.0 and at a space velocity (GHSV) of 100 to100000 h⁻¹ by using the porous catalyst body for decomposinghydrocarbons which comprises at least magnesium, aluminum and nickel insuch a manner that the magnesium and aluminum are present in the form ofa composite oxide of magnesium and aluminum, and the nickel is presentin the form of metallic nickel; and which porous catalyst body has amagnesium element content of 10 to 50% by weight, an aluminum elementcontent of 5 to 35% by weight and a nickel element content of 0.1 to 30%by weight, a pore volume of 0.01 to 0.5 cm³/g, an average pore diameterof not more than 300 Å and an average crushing strength of not less than3 kgf.
 8. A process for producing a mixed reformed gas comprisinghydrogen from hydrocarbons, comprising the step of reacting thehydrocarbons with steam at a temperature of 250 to 850° C., at a molarratio of steam to carbon (S/C) of 1.0 to 6.0 and at a space velocity(GHSV) of 100 to 100000 h⁻¹ by using the porous catalyst body fordecomposing hydrocarbons which comprises at least magnesium, aluminumand nickel in such a manner that the magnesium and aluminum are presentin the form of a composite oxide of magnesium and aluminum, and thenickel is present in the form of metallic nickel; and which porouscatalyst body has a magnesium element content of 10 to 50% by weight, analuminum element content of 5 to 35% by weight and a nickel elementcontent of 0.1 to 30% by weight, a pore volume of 0.01 to 0.5 cm³/g, anaverage pore diameter of not more than 300 Å and an average crushingstrength of not less than 3 kgf and supported on the catalyst body areone or more active metal species selected from the group consisting ofgold, silver, platinum, palladium, ruthenium, cobalt, rhodium, iridium,rhenium, copper, manganese, chromium, vanadium and titanium which havean average particle diameter of not more than 50 nm.
 9. A fuel cellsystem using the porous catalyst body for decomposing hydrocarbons whichcomprises at least magnesium, aluminum and nickel in such a manner thatthe magnesium and aluminum are present in the form of a composite oxideof magnesium and aluminum, and the nickel is present in the form ofmetallic nickel; and which porous catalyst body has a magnesium elementcontent of 10 to 50% by weight, an aluminum element content of 5 to 35%by weight and a nickel element content of 0.1 to 30% by weight, a porevolume of 0.01 to 0.5 cm³/g, an average pore diameter of not more than300 Å and an average crushing strength of not less than 3 kgf.
 10. Afuel cell system using the porous catalyst body for decomposinghydrocarbons which comprises at least magnesium, aluminum and nickel insuch a manner that the magnesium and aluminum are present in the form ofa composite oxide of magnesium and aluminum, and the nickel is presentin the form of metallic nickel; and which porous catalyst body has amagnesium element content of 10 to 50% by weight, an aluminum elementcontent of 5 to 35% by weight and a nickel element content of 0.1 to 30%by weight, a pore volume of 0.01 to 0.5 cm³/g, an average pore diameterof not more than 300 Å and an average crushing strength of not less than3 kgf.